KR20010009467A - Multi-combination linear power amplifier - Google Patents

Abstract

PURPOSE: A multi-connected linear power amplifier is provided to be obtained by two and more analog power amplifier, to reduce a distortion factor significantly and to improve efficiency in the linear power amplifier. CONSTITUTION: The device is composed of two analog amplifier(A1,A2). The analog amplifier(A1) functions as master amplifier and has a lower distortion factor. The analog amplifier(A2) functions as slave amplifier and relatively has high power. A signal source(Vin) is connected to an input of the master amplifier(A1). An output current(io1) from the master amplifier(A1) is applied to the slave amplifier(A2). An output from the slave amplifier(A2) is connected to a point that the output terminal of the master amplifier is coupled to a load terminal(Zo) through a current detector(SN1). A feedback loop(loop1) is formed by detection of the current from the output terminals of the master amplifier(A1), the slave amplifier(A2) and an inductor(L1) to form a negative feedback loop.

Description

Multi-combination linear power amplifier

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear output amplifier having a very low distortion and high efficiency which can be obtained by combining two or more analog power amplifiers, and more particularly to a circuit scheme suitable for an audio power amplifier.

In general, the structure of the audio power amplifier occupies most of the linear heavy amplifier divided into class A, B, AB, etc. according to the structure of the output stage, and recently, switching power amplifier classified into class D has emerged.

These power amplifiers tend to be opposite to each other in terms of efficiency and distortion, and worse in order of class A AB B D in terms of distortion and in the order of D B AB A in terms of efficiency.

If an amplifier with a class A distortion has the efficiency of a class D, it would be the most desirable form, and so recent attempts have been made to combine these analog and digital switching amplifiers.

The advantage of combining two or more analog amplifiers and implementing a new amplifier is that there are many differences depending on the combination method.

1 (a) is a diagram in which two analog power amplifiers are simply connected in parallel. In such a structure, if you balance the two amplifiers well, you will only get twice the power gain, and no other performance improvement can be expected.

Figure 1 (b) is connected to the structure that senses the output current (io1) of the A1 amplifier to adjust the output current (io2) of the A2 amplifier. It can be said to be a connection structure.

However, this structure is difficult to design a feedback loop around the A2 amplifier, and in many cases there is a problem that can not solve the oscillation caused by instability.

Figure 1 (c) is a structure for supplying the current (io2) to the switching power amplifier (SA3) by detecting the output current (io1) of the analog amplifier (A1) as a pulse width modulation (Pulse Width Modulation) output of the switching amplifier Inductor L1 is inserted to filter the waveform.

As such, the structure of combining the switching amplifier and the analog amplifier has been recently patented and published by the present inventor, and is a method for improving efficiency and sound quality at the same time.

However, the disadvantage of such a structure has a problem that switching noise and ripple current appear in the final output (io) depending on the size of the inductance (L1).

The present invention has been made to solve the conventional problems as described above, and relates to a linear output amplifier having a very low distortion and high efficiency, which can be obtained by combining two or more analog power amplifiers, and is particularly suitable for an audio power amplifier. It is about.

1a is a diagram in which two analog power amplifiers are simply connected in parallel

1B is a diagram in which two power amplifiers are connected in a slave relationship;

1C is a diagram in which the analog amplifier A1 and the switching amplifier SA3 are combined in a principal relationship.

FIG. 2A is a diagram in which two analog amplifiers A1 and A2 are coupled in a principal relationship using an inductor L1.

2B is a Bode Diagram illustrating the characteristics of loop 1

3 is a basic diagram of the present invention in which two analog amplifiers A1 and A2 are combined in a feedforward and a feedback;

FIG. 4 is a diagram in which a loop 2 is formed by adding a switching amplifier SA3 and an inductor L2 in FIG. 2.

FIG. 5 is a diagram in which feedforward is added to the circuit of FIG.

FIG. 6A is a diagram in which a differential positive feedback loop proportional to the output current io is formed around the A2 amplifier in the basic diagram of FIG.

FIG. 6B is a diagram in which a differential positive feedback loop proportional to the output current io2 of the A2 amplifier is formed around the A2 amplifier in the basic diagram of FIG.

FIG. 6C is a diagram in which a differential positive feedback loop is formed around an A2 amplifier by winding a secondary winding on an inductor L1 in the basic diagram of FIG. 3.

FIG. 7 is a diagram of adding a differential positive feedback loop to an SA3 amplifier input in the structure of FIG.

8A shows the structure of a basic analog amplifier

8B shows a basic structure of a switching amplifier using pulse width modulation (PWM).

8c shows a basic structure of a switching amplifier using hysteresis

9 illustrates one specific circuit of the analog amplifier.

10 is a connection diagram of an amplifier corresponding to the structure of FIG. 3.

FIG. 11 is a diagram illustrating a configuration in which the output current of the A2 amplifier is detected by using the transformer T1 in FIG. 10, and the differential signals through C1 and C2 are positively fed to the input of the A2 amplifier.

Explanation of the major parts of the drawings

A1, A2: analog power amplifier SA3: switching power amplifier

SN1 ~ SN5: current detection node L1, L2: inductor

CP: Comparator T1: Transformer

d / dt: Differential circuit a1, a2, b1, b2, c1, c2, c3 coupling coefficient

In order to achieve the above object, a feature of the present invention relates to a linear output amplifier having a very low distortion and high efficiency obtained by combining two or more analog power amplifiers, and more particularly to a circuit scheme suitable for an audio power amplifier. A method for combining two types of analog power amplifiers and a method for obtaining new features by combining three types of power amplifiers including a switching amplifier.

Hereinafter, an embodiment of the present invention will be described in more detail based on the accompanying drawings.

FIG. 2A is a preliminary structure of the present invention, in which only two analog power amplifiers are connected to each other, but the inductor L1 is coupled between the output terminal of the A2 amplifier and the output terminal of the A1 amplifier, and the load Zo is outputted from the A1 amplifier. It is configured by connecting at the connection point of the inductor (L1).

It is a new feature that has not been known so far that only two independent analog power amplifiers are combined using an inductor (L1).

In this structure, the output current of the A2 amplifier is controlled proportionally by detecting the output current (io1) of the A1 amplifier at the node SN1, and the A2 amplifier plays the role of the dependent current source controlled in dependence on the A1 amplifier. Can be.

That is, to generate the output voltage of Vo across the load Zo, io current is required. Since io, io1, and io2 have a relationship of io = io1 + io2, if the gain of the A2 amplifier is large enough, If the gain T of the loop L1) is formed through the node SN1 is large enough in the audible frequency band | T | >> 1, then | io2 | 〉〉 | io1 | Since the condition is true, the A1 amplifier can supply a large load current (io) only by supplying a small current.

Therefore, if the feedback loop (loop1) is well designed, the A1 amplifier has a small power and is responsible for the sophisticated waveform amplification, and the A2 amplifier can be operated in a form that is responsible for most of the power output although it is less accurate.

Meanwhile, as shown in the Bode Diagram of the loop gain T illustrated in FIG. 2B, the loop gain T is changed as a function of the frequency (), where the frequency is between 3 dB and unity gain frequency 2. The changing slope is formed at 20 dB / decade under the influence of the inductance L1.

This structure ensures stability. Therefore, the A1 amplifier is designed with a low distortion and sophisticated structure, and the A2 amplifier is designed with high output and high efficiency. A new amplifier that satisfies at the same time is born, and a structure in which only two analog power amplifiers are combined is a feature of the present invention.

On the other hand, Figure 2 has no problem in principle but has one disadvantage. In other words, it is difficult to guarantee reliable operation for a large dynamic input signal due to the characteristics of the nonlinear amplifier.

3 is a basic structure of the present invention for solving such a problem. In FIG. 2A, the output current io1 and the input signal Vin of the A1 amplifier detected at the node SN1 are respectively a1, The gain is adjusted by a2 times, and the added value is applied. Thus, even if a large signal is suddenly applied to the input Vin, the output current io can be controlled more stably than in the case of FIG. It is possible to overcome the nonlinearity of the large signal of loop1.

In such a structure, it is easy to design a loop (loop1) including the A2 amplifier, the inductor (L1) and the coefficient a1, and there is an advantage in that the stability of the feedback circuit can be easily improved.

That is, in FIG. 2, if the gain of loop 1 is not large enough, | io1 | The condition of << | io2 | cannot be satisfied. In other words, in order to design | io1 | to be small enough, the loop gain should be designed large, and as the loop gain increases, the factor of instability increases.

On the other hand, since the fact that the output signal Vout should be a form having a constant gain as a function of the input signal Vin is already determined, the above-described problem can be solved by adding a feedforward path to the input of the A2 amplifier.

The path that adds the input signal Vin by a2 times to the A2 amplifier input of FIG. 3 plays this role, thereby facilitating the design of the loop and ensuring linearity and stable operation even with an instantaneous change and magnitude of the input signal. .

4 to 7 illustrate various forms of complementary development of the basic structure of FIG. 3.

4 is a structure for controlling the output current io3 of the SA3 amplifier by detecting the A2 amplifier output current io2 at the node SN2 based on the configuration of FIG. 3 and having another inductor L2 at the SA3 output terminal. ) Is connected to the output of A2 amplifier, but another loop (loop2) is formed through node SN2. In this case, the load (Zo) current io is given by io = io1 + io2 + io3 and | io1 | 〉〉 | io2 | 〉〉 control with | io3 |

In this type, even if the SA3 amplifier forming the loop 2 is a switching amplifier, the switching ripple generated therefrom is absorbed at the output of the A2 amplifier, so that it is hardly visible at the final output (Vout), so that a clean waveform can be obtained. The SA3 amplifier is left and right, and the precision of the final output waveform is the responsibility of the A1 amplifier, and the A2 amplifier acts as an intermediate buffer.

FIG. 5 shows that the input of the SA3 amplifier is gain-adjusted by the signals detected at the output node SN2 of the A2 amplifier and the input signal Vin by b1 and b2 times, respectively. Even if it is applied, it is a structure to ensure that the output signal which overcomes the nonlinearity of the feedback loop can follow well.

FIG. 6A is a structure in which the output current io is detected at the node SN3 by adjusting the derivative (d / dt) by k times and added to the input terminal of the A2 amplifier. (loop3) was formed, and the nature of this loop3 is different in nature from loop1 and loop2.

First, loop 1 and loop 2 are negative feedback loops, whereas loop 3 is positive feedback loops. Second, loop 3 is fed back through differential circuits, so it is less likely to affect low frequency components and has a higher frequency. The more you influence it.

The role of this loop 3 is to compensate for the characteristics of the inductor L1.

That is, since the characteristic of the inductor L1 has the effect of attenuating the high frequency signal, there is a problem of delaying the response speed when a fast response of the high frequency component is required in the audio frequency band.

The purpose of loop 3 is to compensate for this problem through a differential circuit. In addition, considering that the required current is required differently according to the load (Zo) state, the value is proportionally applied to the load current to differently apply it to actively adapt and respond in spite of the change of load condition. This is the reason why configuration 3 is detected from the output current io (from SN3) and fed back.

FIG. 6B is identical except for one difference with FIG. 6A.

In other words, the differential loop is configured by detecting the inductor L1 current (or the output current io2 of the A2 amplifier), but in fact, the circuit operates under the conditions of | io2 | >> | io1 |. There is no big difference and all of them play a role of canceling the delay effect of the inductor L1 by increasing the response characteristics of the high frequency component.

FIG. 6C differs from FIG. 6B in that a signal is detected from the secondary winding of the inductor L1 and fed back to the input of the A2 amplifier. That is, since the voltage across the inductor L1 appears in proportion to the derivative of io2 current, the secondary winding voltage Vl2 is also proportional to the derivative. Therefore, if only the coefficient a3 value is adjusted and fed back, a differential positive feedback loop is formed.

FIG. 7 is characterized in that the differential current loop is added by detecting the output current io around the SA3 amplifier in the structure of FIG. 4, and in this structure, the current detection point detects the current of the inductor L1 and differentially feedbacks it. The feedback of the inductor L2 current causes a problem due to the ripple of the switching amplifier SA3.

In the following, some circuits for concretely implementing the various structures as described above will be illustrated.

8 illustrates the basic structure of an analog amplifier and a digital switching amplifier.

Fig. 8A shows the form of a basic analog amplifier, and Fig. 8B shows the pulse width modulation in proportion to the positive terminal input signal Vin of the comparator by applying a triangular wave VSG to the negative terminal of the comparator CP. FIG. 8C shows a basic structure of a digital switching amplifier which obtains a PWM output waveform Vout, and FIG. 8C filters the output Vout by applying positive feedbacks R3 and R4 such that the comparator CP has hysteresis. The example in which the PWM output waveform Vout proportional to the input signal Vin is obtained by comparing (R1, R2, C1) is compared.

9 illustrates one specific form of an analog power amplifier.

Here, the following structures will be described with emphasis on the output transistors QA and QB.

FIG. 10 illustrates the structure of FIG. 3 in more detail, and shows one method for detecting an output current of an analog amplifier. Here, the transistors QA1 and QB1 are used to output power transistors QA, The current flowing through QB is detected and the detected current is applied to the input terminal of A2 amplifier by QA2 and QB2. 10 and 3, a1 = RA / RA1 = RB / RB1 and a2 = 1, and the voltage gain Av of the A1 amplifier corresponds to a circuit designed to have Av = 1 + R2 / R1. .

FIG. 11 illustrates a circuit corresponding to FIG. 6B in detail and further illustrates a differential positive feedback loop 3 as compared with FIG. 10.

Here, the current transformer T1 is used as a means of detecting the output current (or inductor L1 current) io2 of PA2, and the voltage across R3 connected to the secondary winding of T1 is differentiated (d / dt) by capacitors C1 and C2. It is converted to a current value and applied to the negative input terminal of the A2 amplifier via QA3, QB3 and QA2 and QB2. Here, the feedback loop is considered in consideration of the polarity of the transformer T1, and it can be seen that a positive feedback loop is formed.

In this way, a more complex multi-coupled structure in which multiple analog amplifiers and multiple switching amplifiers are combined can be configured without difficulty, but all detailed descriptions are omitted since they are similar.

As described above, a feature of the present invention lies in a variety of methods for combining multiple analog or digital switching amplifiers into a multi-structure, where the outputs of each amplifier are connected through one inductor and pass through multiple negative feedback loops and differentiators. It has a feedforward structure in which a positive feedback loop and an input signal (Vin) are connected to the input of each amplifier. Through this configuration, there is an advantage that the minimum distortion and the maximum efficiency can be simultaneously achieved.

Claims (9)

In the amplifier for combining two independent analog amplifiers (A1, A2) to operate as a single unified power amplifier, The role is divided into a sophisticated main amplifier A1 having a low distortion and a relatively large slave amplifier A2, and a signal source Vin is connected to the input of the master amplifier A1, and an input of the slave amplifier A2. Detects and applies the output current io1 of the master amplifier A1 or a signal corresponding thereto, and the output of the slave amplifier A2 is connected to the current detection means SN1 by the output terminal of the master amplifier A1 through the inductor L1. It is connected to the point connected to the load (Zo) terminal through), the feedback loop (loop1) formed by the detection of the output current of the slave amplifier (A2) and the inductor (L1) and the main amplifier (A1) forms a negative feedback loop Multiple coupled linear power amplifier, characterized in that configured to. The method according to claim 1, wherein the output current io1 of the main amplifier A1 or a signal corresponding thereto is detected (SN1), and the value obtained by multiplying a predetermined coefficient a1 by another coefficient (A1) is different from the input terminal of the slave amplifier A2. A multiple-coupled linear power amplifier, characterized in that configured to be added to the input signal (Vin) multiplied by a2). The third amplifier SA3 according to claim 1 or 2, wherein the output current of the dependent amplifier A2 or a signal corresponding thereto is detected, and the input signal Vin is multiplied by a predetermined coefficients b1 and b2, respectively, and added to the third amplifier SA3. The output of the third amplifier SA3 passes through another inductor L2 to the point where the output of the slave amplifier A2 is connected to the inductor L1 through the current detection means SN2. And coupled to form another negative feedback loop (loop2). The slave amplifier (A2) according to claim 1 or 2, wherein the magnitude of the differential signal (d / dt) is adjusted and added to the input terminal of the slave amplifier (A2) after detecting the load current (io) (SN3). And a third feedback loop (loop3) comprising an inductor (L1), the loop forming a positive feedback loop. The multiple-coupled linear power amplifier according to claim 4, wherein the output current io2 of the slave amplifier A2 is detected instead of the load current io to form a positive feedback loop through the differentiator. 4. The multiple coupling of claim 3, wherein a feedback loop is further formed by detecting a load current io or an equivalent current at an input terminal of the third amplifier, and then adjusting the magnitude of the differentiated signal. Linear power amplifier. The multiple-coupled linear power amplifier according to any one of claims 4 to 6, wherein a transformer (T1) is used as the current detection means for forming the differential feedback loop. The multiple-coupled linear power amplifier according to any one of claims 4 to 6, wherein a transformer (T1) is used as the current detection means for forming the differential feedback loop. The multiple-coupled linear power amplifier according to claim 5 or 6, wherein a differential positive feedback loop is formed by a voltage obtained by winding a secondary winding around an inductor (L1).